Method of operating an alkali chlorate cell



Aug. 19, 1969 S. FORBES IIBTHOD 0F OPERATING AN ALKALI CHLORATB CELLOriginal Filed March 30. 1962 FIG. 1

3 Sheets-Shoot 1 INVENTOR. .SYJNEY F0285? Aug. 19, 1969 s. FORBES 26,644

HB'II'IOD OI OPERATING AN ALKALI CHLORA'IE CELL Original Filed larch 30.1962 3 Shoots-Shut 2 FIG. 2.

INVENTOR. JYDNFY FORBES ATTORNEY Aug. 19, 1969 s. FORBES 23,644

METHOD OF OPERATING AN ALKALI CHLORA'I'E CELL mum mm larch so. 1962' aShuts-Shoot. :s

INVENTOR. I I J BY 67M mm United States Patent Oflice Re. 26,644Reiasued Aug. 19, 1969 26,644 METHOD OF OPERATING AN ALKALI CHLORATECELL Sydney Forbes, Mount Lebanon, Pm, asslgnor to Pittsburgh PlateGlass Company, Pittsburgh, Pa., a corporation of Pennsylvania OriginalNo. 3,203,882, dated Aug. 31, 1965, Sac. No. 183,974, Mar. 30, 1962.Application for reissue Aug. 30, 1967, Ser. No. 669,345

Int. Cl. C0111 11/14; Blllk 1/00 US. Cl. 204---95 9 Claims Matterenclosed in heavy brackets I 3 appears in the original patent but formsno part of this reissue specification; mutter printed in italicsindicates the additions made by reissue.

ABSTRACT OF THE DISCLOSURE A method of preparing alkali metal chloratesby electrolysis in an electrolytic alkali metal bipolar cell is ile-.rcribed in which operation the electrolysis is conducted in a pluralityof unit cells spaced apart from each other. The gaseous products ofelectrolysis are collected with brine at the cover which extends overall the units and the brine and gaseous products are passed along thecover surface to a common opening associated with all the cell units.The gaseous products and brine are then passed to a gas collection zoneof reduced cross sectional area in relation to the cell and the gaseousproducts removed therefrom.

The present invention relates to chlorate cells. More particularly, thepresent invention relates to a novel electrolytic bipolar chlorate cellsuitable for use in the manufacture of alkali metal chlorate from alkalimetal chloride solutions. Still more particularly, the present inventionrelates to a novel method for safely conducting the electrolysis ofalkali metal chlorides to produce alkali metal chlorates.

For a complete understanding of the present invention. reference is madeto the accompanying drawing in which:

FIGURE l is a plan view of the top of the novel chlorate cell of thepresent invention showing the positioning of the current distributors,hydrogen outlets and brine feed inlets.

FIGURE 2 is a side elevation partly in section of the cell shown inFIGURE 3 and taken along lines lI-ll of FIGURE 3.

FIGURE 3 is a plan view partly in section of the cell shown in FIGURE 4with the cover removed to show the electrodes and with the electrodespartly removed to show the bottom construction of the cell.

FIGURE 4 is an end view of the cell partly in section showing the busbarconnection to the cell and the liquid produce discharge cduction pipes.

Turning in particular to FIGURES l, 2, and 3, there is shown a covermember 1. The cover member of the cell is bolted to the side 3 by aplurality of bolts 2 which traverse a flange member 11 affined to orformed as an integral part of the side member 3. Between-the covermember 1 and the flange member 11 is a rubber lining l2 and an asbestosgasket 13 to prevent leakage from the side of the cell. Located slightlyabove the upper surface of the cover member 1 of the cell is a brineheader 14. A plurality of feed pipes 15 are integrally connected to theheader 14 and these feed pipes tenninate is downward extensions whichtraverse the cell cover and end as an open tube a short distance belowthe liquid level contained in the cell. Preferably, these feed pipes 15terminate at a level below the surface of the brine contained in thecell of about 6 to 10 inches. The header 14 is fed from a duct 16 whichnormally is connected to a retention tank (not shown), and which islocated at a point some distance from the cell.

The admission of brine to the cell is readily accomplished by suitableconventional pumping mechanisms not shown in the cell drawing. Theadmission of brine to the cell at the various points therein may bereadily regulated by regulating the orifice size of the opening at thedownward extension of the feed pipe 15. Thus, where desired, feed ratesto any one unit within the cell box may be regulated by providing alarger or smaller .orifice on this feed pipe to thereby regulate fluidflow into this portion of the cell.

Located preferably on the opposite end of the cell from the inletopenings 18 for the brine feed are a plurality of hydrogen outlets 19which are in communication with a gas collection zone 20 having areduced cross sectional area in relation to the cross sectional area inthe cell in which it is located. This gas collection zone 20 has a covermember 21 located thereon and this is preferably constructed of apolyvinyl chloride or other similar acid resistant plastic materialwhich is easily fractured and also transparent. In the operation of thecell this gas zone of reduced cross sectional area is partially filledwith liquid depicted as a level 22 in FIG- URE 2 so that a gascollection zone of very small cubic dimension is provided underneath thecover of the cell. Thus, in the event of an explosive range build up ofoxygen in the hydrogen produced in the cell, any explosion will bedissipated by rutpure of the window 21 in the confined gas zone 20. Thesmall cubic area present in zone 20 and the easily rupturable windowthereby considerably minimize the effects of any hazardous accumulationof oxygen in the hydrogen outlets of the cell.

Drawing attention particularly to FIGURE 2, a plurality of anodeconnectors or current distribution rods for the electrodes of the cell31 are shown. These rod members 31 are held in place by a collar member32, preferably constructed of graphite which in turn is held in placewith relationship to the cover of the cell by a clamping member 33. Arubber lining 34 is located beneath the cover surface 1. The entireinterior surface of the cell, that is, the sides and the bottom. islined with various materials to prevent corrosive attack at these brineexposed surfaces. Thus, the side of the cell 39 is lined by a rubberlining 35 which in turn has affixed to the inside surface thereof brickmembers 36. These bricks are preferably constructed of acid resistantceramic materials. Similarly, the bottom of the cell has a rubber lining37 aflixed thereto and this rubber lining has several layers of brickoverlying it. The rubber lining protects the steel surface of the bottomof the cell 38 from corrosive attack during electrolysis. Similarly, therubber lining 35 protects the side members 39 from corrosive attackduring electrolysis. The bricks are placed against the rubber lining toprevent serious corrosive attack of the rubber lining duringelectrolysis by providing a rather tight interface between the rubberand the surface of the brick. In actual operation when fluid leaksthrough the brick and begins attacking the rubber surface the tightphysical connection between the brick and the rubber lining prevents anaccumulative deteriora tion of the rubber lining and ultimately protectsthe steel from corrosion.

As shown in FIGURE 4, busbars 40, used to supply current to the cell ofthe instant invention, are connected through electrical connectors 41 tothe anodes of the cell through the current anode distribution rods 31 byan electrical clamping member 42. The busbars 40, electrical connectors41 and clamping member 42 are preferably constructed of copper and theconnectors 41 are bolted to the clamping members 42 with copper bolts43.

Further. as shown in FIGURE 4 in the bottom portion of the cells. aplurality of spacing members 44 are shown which elfcctively divide thecell into individual units, each unit having a plurality of electrodeslocated therein. The circulation of brine in the cell is thus preferablyon a unit-to-unit basis. this being accomplished by virtue of thespacing members 44. Located in the bottom of each cell unit is anedttcator pipe 45 which removes the liquid products of electrolysis to acommon header 46 located in the bottom of the cell. The header 46 has adischarge condttit 47 connected thereto on the outside portion of thecell and material removed from the cell through this conduit is fed to aretention tank where it is held for a period of time sufficient toconvert the hypochlorou acid contained therein to alkali metal chloratesby a chemical mechanism well understood in the art. A portion of thematerial contained in the retention tanks as has previously beenexplained is returned to the cell along with makeup alkali metalchloride solution for further electrolysis. This portion of theoperation of the chlorate cell is not shown in the drawings since is hasno relationship to the novel method of operating these cells or to theirconstruction.

Turning to FIGURE 2. it is to be noted that the cell is so constructedthat the top member 1 slopes from the gas collection zone to the brineinlet opening 18. The particular pitch of the slope is not of particularconsequence. though preferably an incline providing a drop in a verticaldirection of about #4 inch per running foot or more is preferred. Thesloping top permits the collection of gas bubbles on the undersurface ofthe cover member I at the rubber lining l2 and assists in trans portingthese gas bubbles as they collect at this surface to the gas collectionzone of reduced cross sectional area 20.

The electrode current disttibution rods 3! and their connection to theend blocks 50 of the cell are shown more distinctly in FIGURE 3. In thisfigure there is shown the current distribution rod 31 positioned withina graphite collar 32. The graphite collar 32 is externally threaded andadapted to be received into an internally threa ed graphite end block.The internal threading in the graphite end block is located on the upperend of two bored holes located in the end block and traversing the endblock along its long axis. The bored holes terminate slightly above thelower suri'ace of the end blocks. The current distribution rods 31 arepositioned inside of the collar and are held in place therein and in theend block by tamping amalgam between the outer surface of the rod 31 andthe inner surface of the collar 32 and the bored holes 51. The lateralsurface 52 of the end block 50 is machined on its long axis to providefour elongated channels 53. These channels are constructed and adaptedto receive one end of the electrodes 54 utilized in the cell and aresutticiently long to provide for the insertion of at least seven anodeblades of conxcntional dimension one abme the other.

As shown in FIGURE 3, the electrical current is passed through the cellby introducing current through rods 31 to the end blocks 50. The currentpasses from the end blocks 50 into the inserted end of the electrodes54. The electrodes 54 operate in a bipolar fashion so that currentpasses from one end of the electrode to the other and from here isdistribttted across the electrolyte to the next adjacent electrode whichthen becomes an anode and carries current to the next adjacentelectrode. The electrodes are separated one from the other by virtue ofnon-conducting H spacers 55 located between them. Thus, in operation ofthe cell current will travel from electrode to electrode as depicted bythe small arrows shown in FIG- URE 3. Current distribution rods such asthose shown in the drawing are also located on the other end of the cellwhich is not shown in FIGURE 3. These distribution rods are located inend blocks in exactly the same fashion as those shown in the drawing andat this point current i removed from the cell by passing through theelectrodes into the end block and from the end block into thedistribution rods and from there to the bus system.

In the operation of a cell of this character, because of the physicalrelationship of the current distribution ertd blocks to the first cellunit contained in the cell and the last cell unit contained in the cell.considerably more heat is evolved in the first and last physical unitsformed by the spacing members 44 within the cell. Since this heat of theelectrolyte considerably influences the rate of electrolysis in a givencell unit. brine feed rates to the first and last units of the cell areusually slightl higher than those to the intermediate cells locatedbetween the first and last cells. This may be readily accomplished, aspreviously explained. by regulating the brine orifices feeding the firstand last call units. Usually. this feed rate i such that brine fed tothe first and last unit in the cell is at least 20 percent greater thanthe rate of that utilized in feeding intermediate cells. This is animportant consideration in the operation of a cell of this charactersince if possible. even anode wear from one end of the cell to the otheris the most desirable condition for proper end economical electrolysis.Uniform temperatures throughout the cell help achieve this uniform wear.If desired, current may be reversed in the cell from one end to theother periodically to provide for more even wear of the electrodesduring electrolysis. Even wear of the electrodes during electrolysisprovides a uniform electrode gap across the electrolyte contained withinthe cell and considerably reduces any large voltage fluctuations whichnormally result when large electrode gaps are encountered in this typeof cell.

The electrode materials employed in a cell of this type are normallygraphite and graphite electrodes form the preferred embodiment of theinstant cell. While graphite is preferably employed, it is of course tobe understood that other electrode materials capable of withstanding thecorrosive conditions existing within the electrolyte may also beemployed if desired. Thus, certain base metals uch as titanium andtantalum may be utilized as electrodes when they are provided with asuitable platinum surface on which the electrolysis may take place. Inaddition, various combinations of electrode materials may be employedwhere desired. Thus, if desired, platinum plated or coated titanium ortantalum may be employed as anodes and these anodes provided at one endwith an integral steel cathode so that the entire tructure along theelectrical path of the cell operates as an anode at one end and acathode at the other. The end blocks 50 of the cell are preferablycon-tructed of graphite, usually a corrosion resistant dense graphitematerial such as Karhate. While this is preferred. it is of course to beunderstood that machined steel may also be employed or any otherelectrically conductive metal which can be readily bored and machined topiovide the necessary holes and channels for the electrical connectingrods 31 and the electrodes 54. In this latter case, care must be takento provide for suitable corrosion resistant lining on those surfaces ofthe end blocks which are exposed to brine when placed in the cell.

In the operation of a cell such as shown in FIGURES l4 the cell isfilled to a point such that the electrodes are covered with brine andthe brine level in the cell is at least partially contained in therestricted gas collection zone 20. Electric current is passed throughthe cell via the connectors 31. end block 50. electrodes 54 and theother side of the cell. During electrolysis, brine is fed to the cellthrough header l4 and feed pipes 15 to all of the cell units formed bythe spacers 44. The first and last units in the cell, that is. the unitsadjacent to the electrical distribution system have the orifices intheir feed pipes l5 adjusted to provide a brine how 20 percent greaterthan the other units in the cell. During electrolysis, hydrogen releasedin the cell is caused to collect under the cover of the cell in thebrine. The collected gas bubbles are then transported across the coverby virtue of its upward slope to the restricted gas collection zonewhere it is removed from the cell. Operating the cell in this manner,uniform temperatures are readily provided during electrolysis. Inaddition, the gaseous hydrogen is rapidly collected and removed from thecell.

While this invention has been described with reference to certainspecific embodiments, it is of course to be understood that theinvention is not to be so limited except insofar as appears in theaccompanying claims.

I claim:

[1. In a method of preparing alkali metal chlorates by electrolysis inan electrolytic cell having a bottom, side walls and a cover theimprovement comprising maintaining the cell during electrolysissufiicient brine to maintain brine in contact with the cell cover,collecting gaseous products resulting from said electrolysis on saidcover and transporting them to a gas collection zone of reduced crosssectional area in relation to the cross sectional area of said cell andrecovering said gaseous products from said gas collection zone] [2. In amethod of preparing alkali metal chlorates by the electrolysis of anaqueous alkali metal chloride solution in an electrolytic cell providedwith a bottom, side walls and a cover the improvement comprisingintroducing brine into said cell and removing liquid from said cell atrates Sufi'lClCflt to maintain a brine level in the cell such that thebrine is at least partially in contact with said cell cover, collectinggases produced by said electrolysis on said cover, transporting saidgases along said cover to a gas collection zone of reduced crosssectional area in relation to the cross sectional area of said cell andremoving said gases from said zone] [3. The method of claim 2 wherein abrine level is maintained in said gas collection zone] [4. The method ofclaim 1 wherein a bribe level is maintained in said gas collection zone][5. In a method of preparing alkali metal chlorates by electrolysis ofan aqueous alkali metal chloride solution in an electrolytic cell havinga bottom, side walls and a cover the improvement comprising providingsufficient brine in said cell during electrolysis to maintain brine incontact with said cover. collecting gaseous products of sad electroly ison said cover in contact with brine. transporting said products fromsaid cover to a gas collection zone of reduced cross sectional area ofsaid cell, said gas collection zone being filled in part with brine incommunication with the brine in said cell and removing said gaseousproducts from said zone] 6. In a method of preparing alkali metalchlorate by electrolysis of (m allttlll metal chloride solution in anr'li'ctrolytic alkali metal bipolar chloride cell having a liorrom, sidewalls, a plurality of unit cells positioned therein lllt improvementcomprising providing a cover extending over said unit cells, said coverhaving a continuous opening extending laterally with respect to andunnmunir'uiiug with each of mid unit cells through which opening theproducts of .ralrl unit culls pass from mid bipolar chlorate cell and inwhich opening the prodacts of all said unit cells comingle, maintainingin th cell during electrolysis suflicient brine to maintain brir incontact with the cover, collecting gaseous products resulting from saidelectrolysis on said cover in contact with brine from each of said unitsand transporting said products with brine from each of .raid unit tosaid opening. comingling the brine and gaseous products from each ofsaid units and passing said brine and gaseous products to a gascollection zone of reduced cross sectional area in relation to the crosssectional area of said cell and recovering said gaseous products fromsaid gas colleclion zone.

7. In a method of preparing alkali metal chlorales by the electrolysisof an aqueous alkali metal chloride solution in an electrolytic alkalimetal bipolar chlorate cell provided with a bottom, side walls, aplurality of unit cells positioned therein the improvement comprisingproviding a cover extending over said unit cells, said cover having anopening extending laterally with respect thereto and communicating witheach of said unit cells through which opening the products of said unitcells pass from mid bipolar chlorate cell and in which opening lheproducts of all said unit cells comingle, introducing brine into saidcell and removing liquid from said cell at rates sufiicient to maintaina brine level in the cells such that the brine is in contact with thecell cover, collecting gases produced by cell electrolysis on said coverin contact with brine in each of said units, transporting said gasesalong said cover to said opening, comingling the brine and gases of allsaid units in said opening and transporting said gases to a gascollection zone of reduced cross sectional area in relation to the crosssectional area of said cell and removing said gases from: said zone.

8. In a method of preparing alkali metal chlorares by electrolysis of anaqueous alkali metal chloride solulion in an electrolytic alkali metalbipolar chlorate cell having a bottom, side walls, a plurality of unitcells positioned therein the improvement comprising providing a coverextending over the said unit cells, said cover having an openingextending laterally with respect thereto and in communication with saidcell units, through which opening the products of said unit cells passfrom said unit cells and comingle therein, providing sufiicient brine insaid cell during electrolysis to maintain brine in contact with saidcover, collecting gaseous products of said electrolysis on said coverand in contact with brine in each of said units, transporting saidproducts across said cover to said opening, comingling the gaseousproducts and brine of all of said unit cells in said opening, andtransporting the gaseous products and brine to a gas collection zone ofreduced cross sectional area in relation to the cross sectional area ofthe cell, said gas collection zone being filled in part with brine incommunication with the brine in said cell and said opening and removingsaid gaseous products from said zone.

9. The method of claim 6 wherein gases evolved in the plurality of unitcells are collected at the cover surface and transported along an upwardslope over the cell units to said opening and the gas is separated fromthe brine in said gas collection zone.

It). The method of claim 9 wherein the upward slope is a! the top of thecell.

I I. In a method of preparing alkali metal chlorates by electrolysis ofaqueous alkali metal chloride solutions in an electrolytic alkali metalbipolar chlorate cell having a bottom, side walls and a cover, said cellhaving provided therein a plurality of spaced bipolar electrodesproviding a plurality of cell units in electrical series, theimprovement comprising maintaining in the cell during electrolysissufficient brine to cover the electrodes and mainmin brine in contactwith the cell cover, collecting the gaseous products resulting from saidelectrolysis on said ("over over each cell unit. transporting .ruirlproducts while in eontact with brine laterally over each unit and theelectrodes positioned therein in a direction transversely of the longaxis of the electrodes to a gas Collection zone of reduced crosssectional area in relation to the cross vi'rtional area of said cell andrecovering the gases from 11 plurality of atliaecnt cell units whichwere thereby tulleited in said zone.

1.. The method according to claim I I wherein the crises and brineeollected in said zone are removed therefrom in a direction parallel totlte said series.

13. The method of claim 7 wherein a brine level is nmintnined in Still!gas collection zone.

[4. The method of claim 6 wherein a brine level is maintained in saidgas collection :one.

References Cited UNITED STATES PATENTS The following references. citedby the Examiner. kli'C of record in the patented file of this patent orthe original 8 11/1921 Slater 204-95 11/1965 Collins ct a1. 204-954/1967 Clarke et a1. 204-268 4/1914 Kolsky 204-95 6/1927 Georgi 204-2787/1931 Smith 204-268 2/1932 MCClcnahon 204-268 8 1939 Galusha 220-896/1957 Grafi et a1. 204-95 2/1959 Ferris 204-95 10/1959 Carus 20482FOREIGN PATENTS 5/1951 Belgium.

US. Cl. X.R.

ff UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent NO-Dated 1 figvnlm- Inventor(s) ydney Forbes Column 2, line 4, "is shouldbe --in--.

Column 3, line 37 "is"(2nd occurrence) should be --it--. Column 4, line34 "call" should be --cell--. Column 5, line 70 "chloride" should be--chlorate---.

SIGNED AND SEALED REBZETW (SEAL Attest:

Flewherk WILLIAM E. soHuYLER, JR. Attesting Officer commissioner ofPatents

